The present invention relates to a method of investment casting and in particular to an investment casting system that reduces the amount of pattern material required for the sprue for investment casting.
In investment casting for metals or other materials, a pattern may be made of a volatilizable material such as wax or plastic duplicating the desired cast part. Multiple such patterns may be attached to a sprue providing an inverted tree-like structure of the same volatilizable material having one pattern attached to the end of each branch. The patterns and the sprue are then encased in a flowable mold material, for example, a ceramic material which hardens to form a ceramic shell around the pattern and sprue.
The mold material is heated to melt and volatize the pattern and sprue leaving a hollow central channel with tubular branches leading to cavities corresponding to each pattern (also termed sprues). A casting material, for example molten metal, may then be poured down the central channel to pass to the branches into each of the cavities. When a casting material has hardened, the mold material is removed and the cast parts separated from the sprue.
The pattern material used for the sprue can be relatively expensive and sometimes heavy, thus making handling cumbersome. Because the pattern material for the sprue is ultimately burned out, the pattern material needed to produce the sprue creates additional air pollution. The flowable mold material used for making the mold cavity, selected for strength and for preserving the fidelity of the pattern, may be suboptimal for forming the sprue in terms of weight, strength and cost.